/*
 * @Author: szx
 * @Date: 2021-11-03 18:26:31
 * @LastEditTime: 2021-11-03 18:49:42
 * @Description:
 * @FilePath: \leetcode\400-499\407\407.cpp
 */
#include <iostream>
#include <queue>
#include <vector>
using namespace std;

class Solution {
   public:
    int trapRainWater(vector<vector<int>>& heightMap) {
        if (heightMap.empty()) return 0;
        int m = heightMap.size(), n = heightMap[0].size(), res = 0,
            mx = INT_MIN;
        // 最小堆
        priority_queue<pair<int, int>, vector<pair<int, int>>,
                       greater<pair<int, int>>> q;
        vector<vector<bool>> visited(m, vector<bool>(n, false));
        vector<vector<int>> dir{{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (i == 0 || i == m - 1 || j == 0 || j == n - 1) {
                    q.push({heightMap[i][j], i * n + j});
                    visited[i][j] = true;
                }
            }
        }
        while (!q.empty()) {
            auto t = q.top();
            q.pop();
            int h = t.first, r = t.second / n, c = t.second % n;
            // 最低的海平面
            mx = max(mx, h);
            for (int i = 0; i < dir.size(); ++i) {
                int x = r + dir[i][0], y = c + dir[i][1];
                if (x < 0 || x >= m || y < 0 || y >= n || visited[x][y])
                    continue;
                visited[x][y] = true;
                if (heightMap[x][y] < mx) res += mx - heightMap[x][y];
                q.push({heightMap[x][y], x * n + y});
            }
        }
        return res;
    }
};